Wooden pallet assemblies have been in use for many years in connection with the transportation and storage of a wide variety of products. Palletized loads are typically lifted using a forklift truck or pallet jack and they are moved within storage facilities and to and from transport vehicles, such as trucks, trains and ships.
A typical wooden pallet may support 2,000 to 3,000 pounds of stacked product in the form of boxes, bags or other stackable articles. Since a premium is placed on the rapid movement of palletized loads, forklift operators are under considerable pressure to rapidly insert the forklift tines underneath the pallet, lift the pallet, move it to a desired new location, and disengage from the pallet. This process predictably results in numerous impact loads and high stresses on the wooden members which form the pallet assembly. Similarly, pallet jacks, which include lifting tines and a manually operated hydraulic system, also are rapidly inserted under the pallet and used to lift it so that the operator can manually move the pallet assembly when a forklift truck is not available.
Since there are millions of forklift pallet assemblies in use at any time, and the rapid engagement and disengagement of these pallets by the forklift trucks and pallet jacks causes considerable pallet damage. Splitting of the deck members on the pallet, as well as the longitudinal rails, occurs regularly. In fact, the normal life of a conventional wooden pallet will typically be about three to five round trips or cycles, depending on the care of the forklift operators. A round trip or cycle will be comprised of loading the pallet at a supply center with product, moving the pallet onto a transport vehicle, unloading the pallet from the vehicle at the destination, storing the pallet until the product is used and then returning the unloaded pallet back to the supply center.
Accordingly, in recent years, attempts have been made to manufacture forklift pallet assemblies from polymer or plastic materials which would be less likely to fail under the severe handling conditions which destroy wooden pallets. Typical of plastic forklift pallet assemblies which are currently on the market are the pallets manufactured by Menasha Corporation of Watertown, Wisconsin and the STRUCTO-CELL pallet manufactured by Engineered Polymers Corporation of Mora, Minn.
All plastic pallet assemblies, however, have substantial disadvantages. The plastic pallet often lacks sufficient strength unless it is molded into relatively complex configurations. There is a tendency for plastic to droop under load, particularly when stored on pallet racks, and plastic pallet assemblies are much heavier than wooden assemblies. Another significant disadvantage of plastic pallet assemblies is that the plastic provides a low coefficient of friction. Thus, the plastic load-supporting deck will allow bags, boxes and the like to slide along and even off the plastic deck. When a pallet is tilted or brought to a jarring stop as part of the handling procedure, which often occurs, the load can shift on plastic pallets, whereas it generally will remain substantially in place on a wooden pallet. Plastic forklift pallet assemblies also are more costly to manufacture, although they can have a resulting increased pallet life.
Attempts have been made to overcome the strength and dimensional stability problems associated with polymer or plastic pallets by incorporating wooden members into the polymer structure in order to rigidify the same. Thus, composite wood and polymer pallets have been designed in which wooden members are used as longitudinally or transversely extending strengthening rails in the polymer pallet. Typical of such structures are the pallets shown in U.S. Pat. Nos. 5,123,359, 5,052,307, 4,397,247, 4,145,975 and 3,628,468. All of these pallet assemblies, however, have load-supporting deck surfaces which are plastic. Thus, they suffer from the substantial disadvantage that the coefficient of friction between the load and the load-supporting deck is undesirably low. As can be seen in some of these assemblies, such as the pallets of U.S. Pat. Nos. 5,052,307 and 3,628,468, this problem is attempted to be overcome by providing a rib or a small lip at the edge of the pallet.
In U.S. Pat. No. 4,159,681 a forklift pallet assembly is constructed in which wooden members are used to contain a plastic foam. The pallet also includes a rigidifying arched or flexed wooden member in the pallet core. The cost of fabricating such pallets is undesirably high.
Finally, U.S. Pat. No. 3,126,843 discloses a composite polymer or plastic and wood pallet assembly in which wooden deck members are adhesively secured to longitudinally extending plastic rails. The pallet assembly also includes a container adhesively secured to the rails in lieu of the wooden deck members. Again, however, the wooden deck members of U.S. Pat. No. 3,126,843 are exposed to tines and lifting mechanism of both the forklift truck and the pallet jack. Over 90 percent of the damage done to wooden pallets is to the lead deck boards and ends of the rails. The pallet assembly of U.S. Pat. No. 3,126,843, therefore, also will rapidly become damaged under normal handling conditions.
Accordingly, it is an object of the present invention to provide a pallet assembly and method which provides a pallet having greatly increased durability and strength.
Another object of the present invention is to provide a pallet assembly for a forklift truck or the like which has a load-supporting surface that provides sufficient friction to maintain the palletized load in substantially the same position during normal pallet handling.
A further object of the present invention is to provide a composite wood and polymer forklift pallet assembly which can resist impact loading, has a greatly increased useful life, requires fewer repairs can be constructed using automatic equipment at a reasonable cost, can be made from recycled polymers which can be recycled again, is well suited for rack storage, and will cost less per use cycle.
The composite wood and polymer pallet assembly and method of the present invention have other features and advantages which will become apparent from, and are set forth in more detail in, the accompanying drawing and following description of the Best Mode Of Carrying Out The Invention.